Systems and devices for treating and monitoring water, wastewater and other biodegradable matter

ABSTRACT

The invention relates to bio-electrochemical systems for the generation of methane from organic material and for reducing chemical oxygen demand and nitrogenous waste through denitrification. The invention further relates to an electrode for use in, and a system for, the adaptive control of bio-electrochemical systems as well as a fuel cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. application Ser. No.13/378,763, filed on Feb. 14, 2012, which is a national stage entryunder 35 U.S.C. 371 of International Application No. PCT/US2010/025224,filed on Feb. 24, 2010, which claims the benefit of and priority to U.S.Provisional Application Ser. No. 61/187,469, filed on Jun. 16, 2009,U.S. Provisional Application Ser. No. 61/245,085 filed on Sep. 23, 2009,and U.S. Provisional Application Ser. No. 61/267,594 filed on Dec. 8,2009. The entire contents of each of these applications being herebyincorporated by reference herein.

TECHNICAL FIELD

The invention generally relates to systems and devices for treating andmonitoring water, wastewater and other biodegradable matter, andgenerating value-added products from such matter.

BACKGROUND INFORMATION

The treatment and monitoring of water is a critical societal need.Approximately three percent (3%) of all electricity produced in theUnited States is consumed by wastewater treatment infrastructure. Of theelectricity produced, approximately one and one-half percent (1.5%) isused in the actual treatment of wastewater. Some existing treatmentparadigms include aerobic digestion and anaerobic digestion, however,these paradigms suffer from several drawbacks. For example, aerobicdigestion is an energy intensive process and creates significantbyproducts, such as bio-solids. In addition, anaerobic digestion cannottreat water to levels low enough for environmental release. Thesedrawbacks keep the cost of wastewater treatment high, which therebyaffects a range of industries and municipalities. Thus, there is acritical need for cheaper and more energy efficient wastewater treatmenttechnologies.

Bio-electrochemical systems (BES) are capable of generating electricityor other value-added products from the oxidation and reduction oforganic matter. BES consist of electrodes, such as anode and cathodes,both or individually coated in bio-films with the ability to transfer oraccept electrons from electrodes. Electrodes may also be coated in noblemedals to catalyze one of the reactions taking place. The electrodes canthen be separated by an electrolyte which conveys ions between them(generally a membrane).

Electrodes, bio-films, electrolytes, and catalysts may or may not beenclosed in a casing. Each of these elements, which include the casing,can be connected to external circuits, control systems, or otherreactors for use in combined systems. The geometrical configuration ofthe elements in a microbial fuel cell and their material definition cantogether be defined as the “architecture” of the system.

Over the years, a number of different BES architectures and componentshave been developed and tested for different uses. Two major categoriesof architectures are those that operate in batch mode versusflow-through (or plug flow) mode. In a batch-mode system, an oxidant isplaced in a reactor in batches and is treated until some endpoint isreached before the next batch is treated. In flow-through mode, acontinuous flow of material to be treated is provided into a reactorwith a concurrent flow out of the reactor for a constant volume to beretained inside.

Flow through reactors include side-ways flow or upward flow, such as theupflow microbial fuel cell (UMFC) In a UMFC, an organic-laden medium ispercolated upwards through a porous anode material (i.e. graphitegranules). A number of electrode designs have also been used in UMFCdesigns. Original UMFC designs used in laboratory tests were notscalable due to the use of flat electrode surfaces, which provided lowsurface areas per volume of reactor. Therefore, high surface areamaterials were developed, called a “brush anode”, consisting ofsmall-diameter graphite fibers linked to a central core (generally anon-corrosive metal such as titanium) that provides both highconductivity as well as resistance to fouling. Brush anodes have beenmade of carbon fibers (e.g. PANEX®33 160K) and cut to a set length andwound using an industrial brush manufacturing system into a twisted coreconsisting of two titanium wires. When placed in a reactor, the totalsurface area of typical brush electrodes per volume of reactor has beenestimated to be as high as 9600 m2/m3. Reactors using these brushes haveproduced up to 2400 mW/m2 in a cube reactor with a defined acetatemedium. However, these electrodes are expensive due to the materialsused. In addition, the form itself, a wrapped brush, requires severalsteps to manufacture.

Therefore, a need exists to address the aforementioned drawbacks of theprior art.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to a bio-electrochemical system forthe generation of methane from organic material. The system is comprisedof a reactor that includes an anode, a cathode, a methanogenic microbe,and a power source configured to apply voltage to the anode and thecathode. The anode and the cathode are substantially in proximity withinthe reactor.

In one embodiment according to this aspect of the invention, the voltagefacilitates exocellular electron transfer from the anode to the cathode.In another embodiment according to this aspect of the invention, thesystem is further comprised of a plurality of methanogenic microbes. Inanother embodiment according to this aspect of the invention, thevoltage facilitates exocellular electron transfer to methanogenicmicrobes to initiate a reduction of hydrogen-2 oxidation. In yet anotherembodiment according to this aspect of the invention, methane isgenerated and organic materials are oxidized at either or each of theanode and cathode. The generation of methane and the oxidation oforganic materials serve as the purpose of controlling elements withinthe reactor. The controlling elements include any one or more of thefollowing: the measure of pH, biochemical oxygen demand, chemical oxygendemand, ammonia, and other chemical species. In another embodimentaccording to this aspect of the invention, the reactor is an existinganaerobic digestion system used for wastewater and solids treatment. Theanode and the cathode are placed within the anaerobic digestion systemfor the purpose of enhancing methane production or controlling elementsof an anaerobic digestion process.

In another embodiment according to this aspect of the invention, thepower source is electricity generated by a generator or a fuel cellpowered by methane generated in the reactor. In yet another embodimentaccording to this aspect of the invention, a flow is created within thesystem to move material from the anode to the cathode to increase therate of methane production.

In a second aspect, the invention relates to a bio-electrochemicalsystem for reducing chemical oxygen demand and nitrogenous waste throughdenitrification. The system is comprised of a first chamber, a secondchamber, a methanogenic microbe, and a filter disposed between the firstchamber and the second chamber. The first chamber includes an anode andthe second chamber includes a cathode. The filter is configured tofacilitate nitrification produced therein.

In one embodiment according to this aspect of the invention, the firstchamber includes a first wall and a second wall defining an enclosedspace such that the anode facilitates the oxidization of the microbe. Inanother embodiment according to this aspect of the invention, the secondchamber includes a first wall and a second wall defining an enclosedspace such that the cathode is configured to facilitate the reduction ofnitrates, oxygen or other oxidized species.

In yet another embodiment according to this aspect of the invention, thefirst chamber has a substantially tubular configuration. In anotherembodiment according to this aspect of the invention, the system furthercomprises a membrane for separating the first chamber and the secondchamber. In another embodiment according to this aspect of theinvention, the first chamber is disposed within a first membrane and thesecond chamber is disposed around the first membrane and enclosed by atube member. In yet another embodiment according this aspect of theinvention, the filter is a trickling filter that is placed above theanode to facilitate flow through the anode and over the tricklingfilter.

In a third aspect, the invention relates to an electrode for use in abio-electrochemical system. The system includes a first surface and asecond surface. The first surface is comprised of a substantiallyconductive material. The conductive material is woven to the secondsurface.

In one embodiment according to this aspect of the invention, a membraneis disposed between the first surface and the second surface. In anotherembodiment according to this aspect of the invention, the conductivematerial is woven to the second surface using carpet-manufacturingtechniques and technologies. In yet another embodiment according to thisaspect of the invention, the conductive material is carbon fiber. Inanother embodiment according to this aspect of the invention, the firstsurface has a substantially tubular configuration. In another embodimentaccording to this aspect of the invention, the second surface has asubstantially tubular configuration. In yet another embodiment accordingto this aspect of the invention, the electrode further comprises aplurality of first and second surfaces. In yet another embodimentaccording to this aspect of the invention, the electrode furthercomprises a plurality of membranes.

In a fourth aspect, the invention relates to a system for the adaptivecontrol of a bio-electrochemical system. The system includes a probeconfigured to measure stimulus emitted to a fuel cell, and a controltool for monitoring levels of the fuel cell. The control tool is alsoconfigured to optimize the levels of the fuel cell.

In one embodiment according to this aspect of the invention, the controltool monitors a plurality of chambers within the fuel cell. In anotherembodiment according to this aspect of the invention, the stimulusincludes any one or more of the following: voltage, current, pH,temperature, internal resistance, activation voltage loses,concentration voltage loses, fuel concentration, ammonia levels, nitratelevels, oxygen levels, and oxygen levels. In another embodimentaccording to this aspect of the invention, the levels include any one ormore of the following: voltage, resistance, electrode spacing, fuelloading rate, and pH of fuel.

In a fifth aspect, the invention relates to a fuel cell. The fuel cellis comprised of a first compartment including a cascading anode, asecond compartment including a cascading cathode, and a plurality ofinputs and outputs within each of the first chamber and the secondchamber.

In one embodiment according to this aspect of the invention, the fuelcell includes a substantially tubular configuration in whichmethanogenic or electrogenic microbes are disposed therein. In anotherembodiment according to this aspect of the invention, the firstcompartment is disposed within the second compartment. In yet anotherembodiment according to this aspect of the invention, the first andsecond compartments are disposed within a third compartment including anair-cathode.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameor similar parts throughout the different views. Also, the drawings arenot necessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention.

FIG. 1 is a plan view of a bio-electrochemical system, in accordancewith the present disclosure.

FIG. 2 is a plan view of an embodiment of a bio-electrochemical system,in accordance with the present disclosure.

FIG. 3 is a plan view of another embodiment of a bio-electrochemicalsystem, in accordance with the present disclosure.

FIG. 4A is a perspective view of a fuel cell for use in abio-electrochemical system, in accordance with the present disclosure.

FIG. 4B is a perspective view of an embodiment of a fuel cell for use ina bio-electrochemical system, in accordance with the present disclosure.

FIG. 5A is a plan view of an embodiment of a fuel cell for use in abio-electrochemical system, in accordance with the present disclosure.

FIG. 5B is a plan view of an embodiment of a fuel cell for use in abio-electrochemical system, in accordance with the present disclosure.

FIG. 6 is a perspective view of an embodiment of a fuel cell for use ina bio-electrochemical system, in accordance with the present disclosure.

FIG. 7 is a perspective view of an embodiment of a fuel cell for use ina bio-electrochemical system, in accordance with the present disclosure.

FIG. 8 is a plan view of an embodiment of a fuel cell for use in abio-electrochemical system, in accordance with the present disclosure.

FIG. 9A is a top view of an embodiment of a fuel cell for use in abio-electrochemical system, in accordance with the present disclosure.

FIG. 9B is a cross-sectional view of an embodiment of a fuel cell foruse in a bio-electrochemical system, in accordance with the presentdisclosure.

FIG. 10 is a plan view of a fuel cell for use in a bio-electrochemicalsystem, in accordance with the present disclosure.

DESCRIPTION

Different bio-electrochemical system configurations have been devised tocreate a number of value-added end products. Two of the most importantare electricity and hydrogen gas. Referring to FIG. 1, in abio-electrochemical system 100, electrical current can be created byharvesting electrons 102 liberated during microbial breakdown of organicwastes at an anode 104 while allowing the electrons 102 to flow througha circuit 106 to a cathode 108 exposed to a terminal electron acceptor,usually oxygen. Hydrogen can be generated by purposely applying avoltage to the system 100 while using water as the cathode electronacceptor, which enables hydrogen evolution at the cathode.

In almost all instantiations of microbial fuel cells, the architecturehas been such that the anodic and cathodic compartments are separated bya barrier 110. Often the barrier 110 is an electrically conductivemembrane that can selectively allow ions to pass through it. Conversely,the fluid in the system 100 can be used as the electrolyte in amembraneless configuration. However, in this latter instantiation, anelectron acceptor must be provided, and therefore a region is createdwhere the cathode 108 can either be exposed to the air, or pass thefuel/electrolyte over the barrier 110 where it can then come in contactwith the cathodic 108 while also exposing it to the air or some electronacceptor.

For example, in all configurations in which hydrogen is created, thecathode 108 is assumed to be co-exposed to a different compartment thanthe anode 104 for the hydrogen gas to be evolved. Similarly, in anotherconfiguration, the electrolyte is passed through a loop into the cathode108, before which it can optionally undergo exposure to oxygen in theair.

Referring to FIG. 2, a bio-electrochemical system 200 for the generationof methane from organic material is presented. The system 200 iscomprised of a reactor 202 that includes an anode 204, a cathode 206,and a methanogenic microbe 208. The anode 204 and the cathode 206 aresubstantial in close proximity to one another within the system 200. Thesystem is further comprised of a power source (not shown in Figure) thatis configured to apply voltage to the anode 204 and the cathode 206. Thevoltage facilitates exocellular electron transfer from the anode 204 tothe cathode 206. In addition, the voltage facilitates the reduction ofhydrogen-2 oxidation.

In one embodiment, the methanogenic microbe 208 is biodegraded intothree principal groups within the system 200. For example, the microbe208 may be primary fermentors, secondary fermentors, andhydrogenotrophic methanogens. Each of the microbes 208 may occurindependently of the anode 204 and the cathode 206 in the system 200,however, the incorporation of the anode 204 and the cathode 206 providesan additional mechanism for hydrogen production and/or electrontransport within the system 200. This mechanism provides an enhancedrate of treatment and/or alteration of the composition of the microbe208.

Methanogenic metabolism from carbon-containing wastes, referred to asanaerobic digestion (AD) due to its requirement of anoxic conditions, isa widely-used organic wastewater remediation technology. Its significantbenefits over aerobic waste treatment include the production of methanerich gas (called biogas), lower sludge production, and lower operatingcosts. These benefits have led to its application to diverse organicwaste streams, such as municipal wastewater, agricultural and foodprocessing waste, and chemical industry waste.

Microbe-mediated methane production from complex organic waste streamsis a multi-stage process. In the first stage, the acid-former group(acetogens), which contains many sub-niches, includes species thatdigest polysaccharides, sugars, fatty acids, alcohols and more complexmolecules in the waste into organic acids, primarily acetate, but alsoothers like lactate and butyrate. The second class is themethane-formers, or methanogens, which consist of two sub-niches. Somemethanogens metabolize acetate directly and produce methane as abyproduct (aceticlastic methanogenesis), while the other methanogens useHydrogen-2 (H₂) and Carbon Dioxide (CO₂) as energy sources to producemethane (hydrogenotrophic methanogenesis).

Hydrogenotrophic methanogenesis (HM) is a favorable process within thereactor 202 because of the consumption, rather than production, of CO₂during methane production, which results in a purer biogas with a higherproportion of methane and a lower proportion of CO₂. While CO₂ andacetate are generally abundant byproducts of upstream (acetogenic)metabolic processes, H₂ is a minor byproduct that may quickly becomelimiting and therefore, aceticlastic methanogenesis (AM) can be usedinstead of HM under normal anaerobic digestion operation conditions.Additionally, hydrogenotrophic methanogens are more resistant to hightemperatures (thermophilic conditions) above 50° C. Referring to Table 1below, the HM has a lower Gibbs free energy change than the AM reactionand is therefore thermodynamically favored.

TABLE 1 Routes of methanogenesis. Free Energy Change Reaction EquationΔG° (kJ/reaction) Hydrogenotrophic 4H₂ + CO₂ → CH₄ + 2H₂O −130.7methanogenesis Aceticlastic CH₃COO⁻ + H⁺ → CH₄ + CO₂ −31.0methanogenesis

The system 200 addresses hydrogen limitation in the HM reaction byincluding within the reactor 202 an electrode, or set of electrodes,such as the anode 204 and the cathode 206, that deliver a voltage toincrease the favorability of H₂ formation. In one embodiment, the anode204 and the cathode 206 directly donate electrons to hydrogenotrophicmethanogens to reduce or eliminate the need for H₂ oxidation. Becausethe production of hydrogen in the system 200 occurs at the surface ofthe anode 204 and cathode 206 where methanogenic organism biofilms arepresent, the production occurs in a scale and location that is moreeasily available to methanogenic microbes 208 than it would be if thesimple mixing of hydrogen gas took place within the reactor 202.Further, the hydrogen production and rapid co-consumption within thesystem 200 is inherently much safer than the use of bulk hydrogen gas.

In one embodiment, a microbial electrolysis cell is added within thesystem 200 such that the H₂ evolved at the cathode 206 is produced wheremethanogenic microbes 208 can immediately utilize it for methaneproduction. This is achieved by the addition of sufficient electricalvoltage such that that the cathode 206 potential is negative to allow H₂formation as a terminal electron acceptor for microbial metabolism. TheH₂ that is produced is then utilized by hydrogenotrophic methanogens toproduce methane gas more efficiently.

In another embodiment, an electrode, such as the anode 204 or cathode206, supplying electrons to methanogens microbes 208 is contained in achamber (not shown in Figure), where the cathode 206 potential isprovided such that electrons transferred to methanogens microbes 208 areat a correct energy to allow methane production without the need forhydrogen. In this embodiment, the reactor 202 may be configured as a twochamber reactor, with primary fermentation to produce acetate in thefirst chamber, and secondary fermentation as well as methanogenesisconfined to the second chamber.

In yet another embodiment, hydrogenotrophic methanogenesis is enhancedthrough the production of H₂ by secondary fermentative organismsaccepting electrons from the cathode 206. Additionally, the methanogensmicrobes 208 undergo direct electron acceptance from the cathode 206 toincrease the rate of methane production.

The system 200 may be applied to any anaerobic digestion systems inorder to improve the efficiency, rate of treatment, composition orpurity of biogas produced, or effective wastewater biochemical oxygendemand (BOD) content range. The system 200 can be applied to a widerange of wastewaters and organic matter streams, including, but notlimited to, animal manures or manure slurries; non-manure agriculturalwastes; slaughterhouse waste or wastewater; food processing wastewateror slurries; beverage processing wastewaters, including brewerywastewater or slurries; municipal wastewater; and septic systemwastewater or grey-water building wastewater. The system 200 can also beapplied to existing technology through a retrofit installation, eitheras a custom fabricated system or the application of one or more modularelectrode enhancement units. Electrode enhancement may also be appliedto newly constructed AD systems as a retrofit system or as an integralsystem component.

Referring to FIG. 3, a bio-electrochemical system 300 for reducingchemical oxygen demand and nitrogenous waste through denitrification ispresented. The system 300 includes a first chamber 302, a second chamber304, and a filter 306 disposed between the first chamber 302 and thesecond chamber 304. The filter 306 is configured to facilitatenitrification therein. The first chamber 302 includes an anode 308. Thesecond chamber includes a cathode 310. Methanogenic microbes 312 aredisposed within the first chamber 302 and the second chamber 304. Thefirst chamber 302 is configured to facilitate the oxidization of themicrobes 312 therein. In addition, the second chamber 304 is configuredto facilitate the reduction of nitrite therein. Each of the firstchamber 302 and the second chamber 304 may be separated by a membrane314.

In one embodiment, the system 300 is comprised of four parts: 1) thefirst chamber 302 for microbial BOD oxidation; 2) the trickling filter306 for nitrification of ammonia and nitrite; 3) The second chamber 304for microbial reduction of nitrate to N₂; and 4) the semi-permeablemembrane 314 that separates the first chamber 302 and the second chamber304 topologically, but retains them in electronic and ioniccommunication. The system 300 is used to treat wastewater traveling inone direction through the reactor, in either a continuous orintermittent stream.

The first component of the system is the first chamber 302 that containsan electrode or series of electrodes that serve as the attachment pointfor one or more species of microbes 312. The microbes 312 on theseelectrodes affect the oxidation of carbon based wastes to reduce thebiological oxygen demand (BOD) content of the waste and the transfer ofliberated electrons to the anode. There may be one or more firstchambers that are arranged in series or in parallel configuration.

The second component of the system is the aerobic trickling filter 306that is filled with air or other oxygen-containing gas, and containsnon-conductive, high-surface area substrate over which wastewaterexiting the first chamber 302 can be trickled. Trickling allows rapidre-oxygenation of wastewater for oxidation of ammonia and nitrite tonitrite, also referred to as nitrification. This filter 306 may or maynot include a control system for dynamic monitoring of oxygenconcentration and for adjustment of oxygen concentration to within anoptimal range. In addition, the filter 306 may or may not contain anoxygen-removing device where the wastewater exits the system and entersthe third compartment.

The third component of the system is the second chamber 304 thatcontains an electrode or series of electrodes that serve as theattachment point for one or more species of microbes 312. The microbes312 on these electrodes affect the acceptance of electrons and thereduction of nitrate in the wastewater to N₂ gas which will diffuse outof the liquid upon exit of water from the system 300. There may be oneor more second chambers 304 that are arranged in series or in parallelconfiguration.

The fourth component of the system is the membrane 314 thattopologically separates the first chamber 302 and the second chamber304. The membrane 314 is permeable to protons and small positive ions,but is impermeable to negative ions and uncharged particles. Themembrane 314 serves to keep the first chamber 302 and the second chamber304 in electrical communication in order to complete the circuit, butdoes not allow the passage of wastewater components to bypass the system300.

It is contemplated that the balancing of a number of facets is useful toeffect optimal performance of the system 300. These facets include: (1)the ratio of the first chamber 302 to the second chamber 304 volume andnumber of chambers either arranged in parallel or in series; the ratioof the anode 308 to the cathode 310 electrode surface areas; the flowrate of wastewater through the system 300, as well as continuous vs.intermittent waste flow; the concentration of oxygen and composition ofgas within the trickling filter 306, as well as dynamic addition ofoxygen to the filter 306; the volume ratios of the first chamber 302 tothe trickling filter 306 and the second chamber 312 to the tricklingfilter 306; and the use of computer-controlled system for dynamicmonitoring and adjustment of flow rate, oxygen concentration or oxygenaddition to the system 300.

In one embodiment, the system 300 can be used to treat wastes that arecarbon:nitrogen imbalanced and therefore require carbon, or possiblynitrogen, additions for efficient remediation by other technologies.These wastes include aquaculture wastes, mariculture wastes,agricultural wastes, food processing and beverage processingwastewaters, and other wastes that are carbon:nitrogen-unbalanced. Thesystem 300 may be used on either recirculating or flow throughaquaculture operations.

In another embodiment, microbe 312 co-removal of organic andnitrogen-containing wastes within the system 300 requires carbon tonitrogen ratios of 10:1 to 20:1 to proceed efficiently. Many wastes thatare nitrogen-rich do not readily lend themselves to co-treatment.Aquaculture wastes are an important example of this type of unbalancedwaste, and their balanced treatment is made more imperative by theeffects of ammonia, nitrite and nitrate toxicity on cultured animals.Ammonia and nitrite are toxic at levels well below 1 mg/L, but arereadily treated through an aerobic bacterial nitrification process.However, while nitrate levels of 1000 mg/L are tolerable for manyspecies, it is generally advised to keep nitrates below 1000 mg/L infreshwater or 1500 uM (about 93 mg/L) in seawater, as they aredetrimental to marine invertebrates in closed systems. The resultingdecrease in fish growth rate can cost an aquaculture facility up toseveral millions of dollars per year.

Where nitrate levels are unacceptably high, water can be denitrified bywater exchange or by anaerobic bacteria in a separate treatment system.Anaerobic de-nitrification uses heterotrophic bacteria such asPseudomonas and an additional carbon source such as methanol to reducenitrate to nitrite and eventually to nitrogen gas. This method iseffective but requires carbon source input and frequent chemical balancemonitoring for efficient nitrate removal. Organic matter (e.g. sludge)from the same facility can be used in the place of methanol. However,because the sludge is often in particulate form, hydrolysis andfermentation must be applied to convert the sludge into volatile fattyacids and other molecules more easily consumed by denitrifyingorganisms, adding complexity and cost to the operation.

Alternatively, the facility can use electrochemically generated hydrogengas as electron donor to drive biological de-nitrification. Thisrequires constant input of hydrogen gas bought externally or createdlocally using energy-intensive electrolysis. Another proven approachinvolves the use of plants in artificial wetlands or hydroponic systemsto remove excessive nitrate. The latter adds complexity to theaquaculture system and is not widely used. For these reasons, many farmsto date have ignored the affects of nitrates in order to save money ontreatment, or used water exchange as the principal form ofde-nitrification.

A number of benefits make the system 300 particularly compelling fortreatment of carbon:nitrogen-unbalanced wastes, such as aquaculturewastes. First, a preliminary study suggested that a combinedBOD/de-nitrification reactor run together with a nitrification step.This achieved increased removal yields of 2 kg COD/m³ day, 0.41 kgNO₃—N/m³ day, with a current generation of 34.6 W/m³, all normalized tothe net cathodic compartment, and equally important, they achieved aCOD/N ratio of approximately 4.5 g COD/g N. Since, anodic BOD reductionmay occur at a fraction of sludge production versus aerobic treatmentprocesses, thereby reducing overall treatment costs significantly.Therefore, each of the first compartment 302 and the second compartment304 creates an environment with intensive competition for nutrients andsubstrate attachment sites. These conditions allow probiotic(beneficial) microbes 312, which are more suited to such environments,to survive while fostering a significant reduction in pathogen levelsand improvements in fish health within the system 300.

A number of factors may suggest that BOD removal can be achieved usingcarbon:nitrogen-unbalanced wastes, such as aquaculture wastes at theanode 302. First, as described above, necessary bacteria are alreadypresent in wastes. For example, one study showed a reduction of up toeighty-four percent (84%) of the BOD from cow manure slurry, whileanother study consistently achieved BOD reduction of eighty-percent(80%) using domestic wastewater. Further, another study demonstratedthat swine waste could produce electricity in a microbial fuel cellsystem (MFC) at power densities consistent with other potentialsubstrates using air-cathode MFC systems. These systems measured amaximum power density of 261 mW/m² while reducing soluble chemicaloxygen demand (COD) by 88%-92% percent and ammonia by 83%. Additionally,a number of electrogenic bacteria isolated from freshwater and marinesediments, demonstrating that these species thrive in aquaculture systemconditions.

BOD reduction within system 300 is accomplished with significantly lessexcess biomass production compared to equivalent aerobic processes.Under aerobic conditions, the consumption of 1 g of organic substrateproduces around 0.4 g of biomass; in an MFC the same amount of BODreduction proceeds with 50-80% less biomass production observed. Onestudy documented even lower biomass yields in an MFC process undercertain conditions. Given that sludge treatment at a municipal wastetreatment facility can cost $1,000 per ton of dry waste, this couldamount to a substantial reduction in cost and a more favorable costbalance for the BEC process.

Many early studies of BEC processes focused on anodic processes, usingtraditional platinum-coated, open-air cathodes. One study notedbio-cathodic oxygen reduction in open-sea systems. Another studydemonstrated high current production using an acetate-fed fuel cell witha graphite felt open-air biological cathode 83±11 W m-3 MFC (0.183 LMFC) for batchfed systems (20-40% coulombic yield) and 65±5 W/m-3 MFCfor a continuous system with an acetate loading rate of 1.5 kg COD m-3day-1 90±3% coulombic yield). These study found that by adding manganeseto air-cathode, power output increased substantially. Other studiesconfirmed cathodic bacteria's role as a true oxygen catalyst.

Biological cathodes reduced electrode cost by avoiding previous metalcatalysts. Perhaps as importantly for water treatment applications,biological reduction can be harnessed to perform additional treatmentsteps. De-nitrification is a prime target because the reductionpotential on the order of that of oxygen (NO₃/N₂ at +0.74V versus+0.82Vfor O₂/H₂O). One study was able to demonstrate increased denitrificationin the presence of biological cathodes (55.1% increase at 100-200 mV andcurrent of 40 mA), though this was accomplished using poised potentialsrather than full MFC processes. More recently, combinedBOD/de-nitrification was demonstrated in complete microbial fuel cellsystems operating with biological cathodes.

Another proposed study recently demonstrated a combinedBOD/de-nitrification reactor running together with a nitrification step.This study achieved increased removal yields of 2 kg COD/m3 day, 0.41 kgNO₃—N/m3 day, with a current generation of 34.6 W/m3 all normalized tothe net cathodic compartment. Equally important, the study achieved aCOD/N ratio of approximately 4.5 g COD/g N, as compared to the typicalrequirement ratio of 7, a value which virtually eliminates the need forcarbon addition in wastewater treatment. The system 300 combines theconcept of looping nitrification together with other advances made inthe field to achieve an economically superior combined carbon-nitrogentreatment.

In one embodiment, the system 300 is a two-chamber system (the firstchamber 302 and the second chamber 304), where the anode 308 and thecathode 312 are separated into two chambers by the membrane 314 thatallows ion exchange. In another embodiment, the system 300 is a singlechamber system using air at the cathode 312, which can utilize either achemical catalyst or a biologically-catalyzed cathode.

Both single and two-chamber systems can be operated in batch orflow-through mode. A variation on the flow-through MFC, called an upflowMFC (UMFC), addresses transport limitations and it has been shown tooperate with lowered internal resistance than a conventional MFC. In theUMFC, organic-laden medium 312 is percolated upwards through a porousanode 312 material (i.e. graphite granules). In one study, the MFC waspartitioned with a proton exchange membrane, placing an air-exposedcathodic chamber above the anode 308. In this study, defined sucrosemedium was used to test the UMFC. High SCOD removal rates were observed(up to 97%) even at relatively high loading rates over 3 g COD/L/day,though a majority of this could be attributed to methanogenesis ratherthan electron transport. A second study undertaken with another UMFCdesign showed that a lower internal resistance increased volumetricpower production to a maximum of 27 W/m³. More recently, a pilot scaleupflow MFC was developed and demonstrated by running on breweryeffluent.

Referring now to FIGS. 4A, 4B, 5A, 5B, 6, 7, 8, 9A, and 9B, an electrode400 for use in a bio-electrochemical system is presented. The electrode400 includes a first surface 402 and a second surface 404. The firstsurface is comprised of substantially conductive material 406 that iswoven to the second surface 404. A membrane 408 may be disposed betweenthe first surface 402 and the second surface 404. The conductivematerial 406 may be, for example, carbon fiber. In one embodiment, asshown in FIG. 5A, the first surface 402 has a substantially tubularconfiguration. In another embodiment, as shown in FIG. 5B, the secondsurface 404 has a substantially tubular configuration. As shown in FIGS.6 and 7, the electrode 400 may also include a plurality of first andsecond surfaces as well as a plurality of membranes.

The electrode 400 may be comprised fabricated from any material 406 withsuitable physical and electrical properties. These properties include,but are not limited to, electrical conductivity, flexibility/stiffness,catalytic properties, and biological compatibility. The base weave ofthe material 406 may be made of a different material from its loops ortufts. For example, a different material may be used because it ischeaper and/or a better conductor of electricity. Additionally, a basematerial 406 may be used for the electrode 400 with a specialty coatinglayer applied to enhance the electrode's 400 performance.

The electrode 400 may also be made from a variety of sizes. The shape ofthe electrode 400 may be varied as well. The electrode 400 may includeseveral characteristic dimensions, such as length, width, depth, fabricweave size (grid spacing), and tuft/loop spacing and density. Thesedimensions will have direct impact on the performance of the electrode400 and will be optimized to meet the specific demands of the electrode400. Further, any type of construction technique may be used for thefabrication of the electrode 400. These techniques include, but are notlimited to, needle punching, tufting, axminster, durcam, woven, knitted,rivet head, fusion bonded, and flocked. The specific constructiontechnique used will depend on the materials and exact specifications ofthe electrode 400.

In one embodiment, the electrode 400 may be provide with a dielectricmaterial 406 in order to divide the electrode 400 into differentchambers. The material 406 can serve to selectively allow thetransmission of certain soluble chemicals on the basis of size,hydrophobicity, charge, and other properties. The material 406 may be,for example, a sheet polymeric membrane. In order to minimize systemspace, the membrane may be adhered directly onto the bottom of theelectrode 400. This material 406 provides structural support as well asphysical separation and selective transport. In another embodiment,

For the case of a fuel cell in which ion transport is essential,minimization of distance from the electrode to the selectively permeablemembrane decreases the distance, time, and driving force required fordiffusion. Therefore, in another embodiment, this construct can be usedwithout modification in planer geometry and can be used in combinationwith any other type of electrode 400.

Referring to FIG. 5A, the electrode 400 is comprised of a substantiallytubular configuration. This configuration may be accomplished by rollingthe material 406 with the second surface 404 on the exterior, therebycreating an external tubular electrode 400. This provides forcompartmentalization, which is useful in many reactor configurations. Ause of this construct would be to use one side of the electrode 400(inside or outside) as a cathode and the other side as the anode in afuel cell.

In one embodiment, the electrode 400 can be utilized in a system that iseither batch or continuous. The working fluid on either side of themembrane may be gaseous or liquid. The liquid may flow from one sectioninto the other or have no connection. The flow may be in the same oropposite directions and the tube may be oriented in any desireddirection. With the external tubular electrode 400, any other electrodemay be used on the inside of the electrode 400.

Referring to FIG. 5B, like the electrode of FIG. 5A, the electrode 400is comprised of an internal tubular architecture by rolling the material406 with the first surface 402 on the interior. Electrode 400 providesfor compartmentalization and its use is similar to the electrode of FIG.5A.

Referring to FIG. 6, the electrode 400 may be modified to incorporateadditional electrodes by placing additional electrode(s) 410 on the backside of the first layer 402. Thus, the back side of the first layer 402becomes an intermediate layer 408. The dielectric material 406 providesthe same functions (support, containment, selective transport) as theelectrode of FIG. 5A, but also provides direct electric insulation tothe electrode 400 to avoid a short circuit between the two electrodes.Either electrode can still be used for any desired reaction. Thearchitecture of the electrode 400 and the electrode 410 minimize thedistance between the two electrodes for accelerated ion transport whilesimultaneously maximizing the surface area of the electrode. Electrondonation occurs at one electrode while electron accepting occurs at theother electrode. It is contemplated that the electrical potential of thedonating electrons does not need to be higher than that of the acceptingelectrons if a power source is placed between the electrodes.

Referring to FIG. 7, the electrode 400 may include multiple layers ofstacked electrodes to form a series of chambers. In one embodiment, theanode and cathode (not shown in Figure) electrode 400 reside in the samechamber throughout the surface of the electrode 400. Specifically, thesame type (anode or cathode) can be wired together or separatelydepending on the reactor performance. Electrode 400, can facilitate flowin any direction and has the benefit of large surface area, highthroughput, and the capability of achieving a higher volume withoutsacrificing close electrode spacing.

Referring to FIG. 8, the electrode 400 may have a substantially tubularconfiguration such that either side of the electrode 400 may be used asa cathode or anode. Further, electrode 400 may be operated in a batch orcontinuous flow, its orientation may be in any direction, and it mayutilize liquid or gas in either its first layer or second layer. It iscontemplated that multiple electrodes 400 may be connected in series orparallel. The wiring may connect the electrodes 400 and the differentsections depending on the specific application. Further, the concentricelectrode 400 may be used with or without an exterior casing, dependingon the specific application.

In another embodiment, the incorporation of multiple concentricelectrodes 400 into a single reactor results in the production of ashell and tube electrode reactor. This reactor may contain any number ofelectrodes 400 contained within the shell. As with any shell and tubereactor, the flow may co-flow, counter-flow, or cross-flow. Further,both the tube and the shell side may contain as many passes as desired.Flow may be connected between the two electrodes 400 or unconnected. Inaddition, the sections and different electrodes 400 may be wired asneeded. The shell and tube electrode reactors makes full utilization ofspace by packing as much reactive surface area as possible into thesmallest volume.

Electrode 400 may find a variety of applications. In one embodiment, thehigh specific surface area makes the electrode 400 ideal for fuel cellapplications. Fuel cells are often limited by the area available tocatalyze the reaction and by sizes which can be used while maintainingefficiency. The electrode 400 simultaneously maximizes surface area andminimizes electrode separation, thus optimizing the fuel cell.Electrodes 400 are suitable for use in all types of fuel cells. Thematerial of the electrode 400 needs to be selected with the specificelectrode and application in mind.

In another embodiment, the electrode 400 may be utilized to increase theproductivity of batteries. If the battery is limited by the rate of theelectrode, the electrode 400 may increase current. Electrode 400 mayalso be used for any reaction which requires separated oxidation andreduction steps. Any reactor which makes use of a redox reactor has thepossibility to be utilized with the electrode 400. This allows forseparation of the half reactions which may allow energy extraction orminimization of energy input. Additionally, this may limit the formationof by-products from side reactions. In addition, the naturalcompartmentalization of a reactor utilizing the electrode 400 carriesthe benefit of reduced separations requirement. The electrode 400 iscapable of providing electrons (with or without associated ions) into awell-defined environment, thus enhancing the chemical purity of theproduct. Alternatively, the electrode 400 can act as an electron sink toremove electrons from a system.

In yet another embodiment, biological catalysis may be used with theelectrode 400. The electrode 400 maximizes the surface available formicrobial attachment. In this application, electrode materials arechosen to be biocompatible with specific attention to attachmentproperties. Microbial fuel cells are one application of biologicalcatalysis with the electrode 400, but this is not the only process.Biology, especially microbiology, has an extremely diverse set ofmetabolic capabilities. These unique and efficient processes can beutilized in a reactor with the electrode 400 to produce and convert notonly energy but also a wide variety of chemicals from simple to complex.

Further, any application which utilizes an electrode for the transfer ofelectrons may utilize the electrode 400. More complex devices buildingupon electrodes may be also constructed with the electrode 400.

Referring to FIG. 10, a fuel cell 500 is presented. The fuel cell 500 iscomprised of a first compartment 502, a second compartment 504, a thirdcompartment 506, and a plurality of inputs and outputs within each ofthe first compartment 502 and the second compartment 504.

The first compartment 502 includes a cascading anode electrode and thesecond compartment 504 includes a cascading cathode electrode. The fuelcell 500 may have a substantially tubular configuration. In addition,the first compartment 502 may be disposed within the second compartment504. Further, the first compartment 502 and the second compartment 504may be disposed within a third compartment 504, which includes anair-cathode.

Fuel cell 500 may be designed for use with existing anaerobic digester(AD) systems. For example, the fuel cell 500 can create a cascadingseries of electrogenic enhanced AD reactors in which the placement ofelectrodes, applied voltages, and other attributes of the fuel cell 500are designed to optimize methane production. In one embodiment, thecascading chambers can be designed to alternate between anode andcathode electrodes. For example, the chambers may be designed toalternate between biological anodes or cathodes and chemical anodes orcathodes. Each compartment of the fuel cell 500 may have a differentapplied voltage, thereby enabling more complete wastewater treatment atlower cost.

In one embodiment, two electrodes may be used with the fuel cell 500 toretrofit with existing anaerobic digesters by taking the power from agenerator to enhance anaerobic digestion, both in terms of the speed ofthe process and the level to which water may be treated. Becauseexo-electric bacteria oxidizes organics in wastewater to lower levelsthan methanogensis, the fuel cell 500 can clean more water using thisprocess than with standard AD systems.

In another embodiment, the fuel cell 500 may control the pH of flowwithin its compartments. This process may be accomplished by modulatingthe applied voltage, and other aspects of the fuel cell 500 to ensurethe pH remains in the right range for anaerobic digestion, thusoptimizing methane production. Further, this pH modulation can be usedin combination with another bio-electrochemical system using computersand measurements from the elements of the fuel cell 500.

In another aspect of the invention, a system for the adaptive control ofa bio-electrochemical system is presented. The system is comprised of aprobe configured to measure stimulus emitted to a fuel cell and acontrol tool for monitoring levels of the fuel cell. The stimulus maybe, for example, any one or more of the following: voltage, current, pH,temperature, internal resistance, activation voltage loses,concentration voltage loses, fuel concentration, ammonia levels, nitratelevels, oxygen levels, and oxygen levels. The control tool is configuredto optimize the levels of the fuel cell. The levels may include any oneor more of the following: voltage, resistance, electrode spacing, fuelloading rate, and pH of fuel.

It is contemplated that the system can be used to tune various zones ofa fuel cell independently. In one embodiment, the system furtherincludes multiple resistors. The system also includes automated feedbackcontrol which can be used to maintain various levels within the system.For example, the automated feedback control allows control over theappropriate pH in an operation of a traditional anaerobic digester, oran enhanced anaerobic digester. The pH change can be implemented bychanging some aspect of the bio-electrochemical system and thus the rateat which it operates, such as the resistance between electrodes or theapplied voltage. In another embodiment, the activity of thebio-electrochemical system can be used to sense and monitor pH throughthe use of buffers, such as lime for enhanced performance.

It will be understood that various modifications may be made to theembodiments disclosed herein. Therefore, the above description shouldnot be construed as limiting, but merely as illustrative of someembodiments according to the invention.

What is claimed is:
 1. A method for adaptively controlling an anaerobicreactor system comprising: adaptively controlling one or more parametersthat effect an anaerobic reactor based on one or more measurements ofreactor electrodes, wherein the electrodes comprise an anode and cathodeand one, or both, of the electrodes is configured in proximity to atleast one electrically active microbe, and wherein one of the parameterscomprises a reactant loading rate.
 2. The method as in claim 1 whereinthe one or more parameters further comprise a temperature, a voltage, ora resistance and the one or more measurements comprise a current, avoltage, an internal resistance, an activation voltage loss, aconcentration voltage loss, or a fuel concentration.
 3. The method as inclaim 1 further comprising: adaptively controlling the measurement ofone or more of the following: a temperature, a current, a voltage, aninternal resistance, an activation voltage loss, a concentration voltageloss, and a fuel concentration; and adaptively controlling the one ormore parameters based on the one or more measurements.
 4. The method asin claim 1 wherein the anode electrode is configured in proximity to theat least one electrically active microbe.
 5. The method as in claim 1wherein the anaerobic reactor system comprises a bio-electrochemicalsystem.
 6. The method as in claim 1 wherein the anaerobic reactor systemcomprises a fuel cell.
 7. The method as in claim 1 further comprisinggenerating methane using the anaerobic reactor.
 8. The method as inclaim 1 wherein a reactant associated with the reactant loading ratecomprises an organic waste consumed to generate methane.
 9. A method foradaptively controlling an anaerobic reactor system comprising:adaptively controlling one or more measurements of electrodes of ananaerobic reactor associated with one or more parameters that effect theanaerobic reactor, wherein the electrodes comprise an anode and cathodeand one, or both, of the electrodes is configured in proximity to atleast one electrically active microbe, and wherein one of the parameterscomprises a reactant loading rate.
 10. The method as in claim 9 whereinthe one or more measurements comprise a temperature, a current, avoltage, an internal resistance, an activation voltage loss, aconcentration voltage loss, or a fuel concentration, and the one or moreparameters further comprise a temperature, voltage, or a resistance. 11.The method as in claim 9 wherein the one or more parameters furthercomprise a temperature, a voltage, or a resistance, and the methodfurther comprises adaptively controlling the measurement of one or moreof the following: a temperature, a current, a voltage, an internalresistance, an activation voltage loss, a concentration voltage loss, ora fuel concentration.
 12. The method as in claim 9 wherein the anodeelectrode is configured in proximity to the at least one electricallyactive microbe.
 13. The method as in claim 9 wherein the anaerobicreactor system comprises a bio-electrochemical system.
 14. The method asin claim 9 wherein the anaerobic reactor system comprises a fuel cell.